Pest controlling

ABSTRACT

The present invention features a sustained-release microcapsule for long-term pest controlling. In general, a microcapsule has a capsule core including active pest-control ingredients and diluents, and a capsule shell which physically separates the capsule core from the surrounding medium. Diluents are arranged to entrap active ingredients therein and to provide resistance to mass transfer of the active ingredients therethrough. The capsule shell generally includes the shell pores and provides additional resistance to mass transfer of the active ingredient therethrough. Diluents are selected from a class of material such that the mass transfer resistances existing in the capsule core and/or capsule shell depend on the temperature of the surrounding medium.

[0001] This invention relates to pest controlling and more particularlyto a sustained-release, long-term pest-control microcapsule which isenvironmentally friendly and non-toxic.

[0002] Use of microcapsules containing various active pest-controlagents is well known. Several patents disclose such microcapsules, e.g.,U.S. Pat. No. 3,429,827, 3,577,515, 4,280,833, 4,285,720, 4,417,916,4,900,551, and 4,936,901. Interfacial polycondensation is often used asthe technique to form microcapsules loaded with active pest-controlagents, although techniques including complex coacervation and in situpolymerization can also be used. These and other microencapsulationtechniques for preparing microcapsules have been described in variousreview articles. Microencapsulation, Thies, C., Kirk-Othmer Encyclopediaof Chemical Technology, 4th ed., Vol. 16, John Wiley, NY, 1995, pp628-652. Microcapsule Processing and Technology, Kondo, A., (edited andrevised by J. Wade van Valkenburg), Marcell Dekker, NY, 1979.Mikrokapseln, Sliwka, W., Ullmmanns Encyklopadie der technischen chemie,Vol. 16, Verlag Chemie, Weinhein, 1978, pp 675-682.

[0003] It is an important object of the invention to provide improvedmethods and means for pest controlling.

[0004] The invention features a sustained-release, long-termpest-control microcapsule which prolongs its potency adaptive to thetemperature of the surrounding medium and which is environmentallyfriendly and nontoxic.

[0005] One aspect of this invention relates to a pest-controlmicrocapsule which releases an active pest-control agent at a sustainedrate, thereby prolonging the potency of the microcapsule. In general, amicrocapsule includes a capsule core and a capsule shell. Historically,it has not been recognized that both the shell and core can provideresistant paths to the mass transfer of active pest-control agentcontained in the capsule core. The pest-control microcapsule of thepresent invention utilizes this new concept, thereby reducing the rateof release of active ingredient distributed to the surrounding medium,thereby extending the length of performance of the capsules in thefield, and reducing the cost of pest control as well as the potentialfor environmental pollution. Furthermore, candidate diluents arebiodegradable materials compatible with the environment.

[0006] The diluent is distributed in the core in such a manner that theactive pest-control agent is effectively bound by the diluent anddiffuses through the resistant paths formed by the diluent to reach thecapsule shell through which it then diffuses. The diluent may form asolid-like, matrix-like or mesh-like structure inside the core andentrap the active ingredient inside such matrix and mesh. The diluentmay also simply form a homogeneous solution with the active ingredient(AI) in which the AI and diluent interact (i.e., AI-diluentinteraction), thereby slowing release of the AI from the capsule.Accordingly, a formulator can obtain desirable permeability or releaserate of the active ingredient by manipulating several factors, such asthe amount or percentage of the diluent contained in the capsule core,distribution pattern of the diluent in the core, method of entrappingthe active ingredient in the diluent, and other physical properties ofthe diluent.

[0007] The capsule shell separates the core volume material from thesurrounding medium, and is arranged to provide additional resistantpaths to diffusion of the active ingredient from the capsules. Thus,permeability or release rate of the active ingredient can be manipulatedby controlling several features of the shell such as pore size, length,density, tortuosity, pattern of pore distribution, and other physicalproperties of the material composing the shell.

[0008] A pest-control microcapsule can be composed in such a way thatthe permeability or release rate of the active ingredient depends uponthe physical and/or chemical properties and melting point of the diluentand the temperature of the surrounding medium. Lipids such as oils,waxes, and fats with at least one ester linkage or cholesterol are usedas diluents and incorporated into the capsule core throughmicroencapsulation. In general, these lipids have melting points of 80°C.-90° C., but some lipids may form liquids at room temperature. Meltingof lipid solids may occur over a wide range of temperature, especiallywhen the diluent consists of a mixture of various lipids with differentmelting points or when those lipids are solids at or just below roomtemperature (e.g., 20°-30° C.). When the temperature of the surroundingmedium rises near or above the melting point of the lipid, i.e., usuallyduring the season and/or the time of the day with high insect activityor mating, the lipid diluent begins to soften or melt, and the activeingredient previously entrapped by the solid diluent is able to diffusefrom the capsule at a higher rate. However, when the temperature fallsbelow the melting point of the lipid and enough to suppress insectactivities, the lipid diluent hardens or solidifies and effectivelysustains the release of the active pest-control agent by re-entrappingthe agent in the hardening or solidifying lipid.

[0009] In general, the lipid has a relatively high boiling point, e.g.,higher than 200° C. at atmospheric pressure and, therefore, hardlyevaporates. Accordingly, the potency of the pest-control microcapsulecan be effectively prolonged adaptive to the temperature of thesurrounding medium. It is appreciated that lipids capable of prolongingfunctionality of the capsules may melt below room temperature. In thiscase, the lipid-active ingredient interactions alone in the liquid stateprolong release of the active ingredient from the capsules. That is, thepest-control microcapsule includes, in its core, a lipid diluent that iscapable of dissolving the active pest-control agent in liquid state toform a homogeneous solution at room temperature (20°-30° C.). By mixingsuch diluent with the active ingredient, a formulator can effectivelyentrap the active ingredient within the lipid diluent. When using lipiddiluents that are solids at the room temperature, the formulator cancustomize the melting point of the diluent by manipulating the molecularsize and chemical structure of the lipid. For example, the melting pointof the lipid including oils, waxes, and fats can vary over a wide rangeof temperature by manipulating the number of ester linkages as well asthe number and characteristics of the short-, medium-, and long-chainedfatty acids attached to those ester linkages.

[0010] Lipids with aforementioned properties can be obtained from avariety of sources, including minerals, plants, and animals, and may bemanufactured by chemical synthesis. Such lipids may be used in theirnatural form or may be treated by mechanical or chemical processesincluding filtration, purification, distillation, hydrogenation, andselective crystallization. Examples of those lipids include mineral oil,plant oil, animal oil, animal fat, butterfat oil, butter fat, lard,natural wax, beeswax, insect wax, candellila wax, carnauba, hydrogenatedtallow or various plant oils, paraffin wax, and the like. Yet otherexamples of such lipids include monoglyceride, diglyceride, andtriglyceride such as tristearin, tripalmitin, and trilaurin, with orwithout a free fatty acid.

[0011] The sustained-release, pest-control microcapsule of the presentinvention can be composed of biodegradable and nontoxic compounds. Thepest-control microcapsule can include in its core a biopesticide (suchas pheromones, pyrethroids, insect growth regulators, and insectattractants or repellents) and an inactive, biodegradable and non-toxiclipid diluent (such as oils, waxes, and fats with ester linkages orcholesterol). However, conventional toxic pest-control agents can alsobe used along with the inactive, biodegradable, and nontoxic lipiddiluent.

[0012] The pest-control microcapsule of the present invention can have adensity lighter than or comparable to that of water. Generally, lipiddiluents are lighter than water and, therefore, microcapsules containingsufficient amount of such lipids float in an aqueous solution onstorage. The creamed layer formed by clogged microcapsules may adverselyaffect the potency and performance characteristics of the microcapsules,unless the capsule slurry is properly formulated. Accordingly, awater-immiscible compound, having at least one ester linkage and havinga density greater than that of water, may be added to the lipid diluentin an amount effective to make the microcapsules sink slowly in anaqueous solution or suspending medium. Such water-immiscible compoundscan also be added in an amount effective to achieve natural buoyancy ofthe microcapsule. Examples of such dense lipids include, but are notlimited to, triethyl citrate, tributyl citrate, and triacetin.

[0013] The pest-control microcapsule of the present invention can alsoinclude an antioxidant in the diluent. Addition of an antioxidationagent enhances the oxidative stability of the diluent and, therefore,prolongs potency of the microcapsule as well. Examples of suchantioxidation agent include vitamin E oil and synthetic food-gradeantioxidants. Sun screen (such as carbon black or other UV absorbers)can also be added in order to provide protection from sun light.

[0014] The microcapsules of the present invention can be formed byprocesses, such as complex coacervation, solvent evaporation,interfacial polymerization (IFP), or in-situ polymerizationencapsulation protocols. With IFP protocols, multi-functional acidchloride and isocyanate are employed as shell-forming agents. When theactive pest-control agent contains a functionality readily reacting withacid chloride or isocyanate, microcapsules can be formed by complexcoacervation, in situ polymerization or solvent evaporation.

[0015] In another aspect, this invention features a method of long-termpest control. The steps of the method include mixing an activepest-control agent with an inactive, biodegradable, and nontoxic diluentto the extent effective to entrap the active ingredient by the diluent;microencapsulating the mixture to form a microcapsule with a capsulecore and shell; providing resistant mass transfer paths for the activeingredient in the capsule core and the shell; and sustaining the rate ofrelease of the active ingredient through the core and the shell. Inparticular, the new method can accomplish better entrapping of theactive ingredient by dissolving the active ingredient in the diluent inliquid state, and entrapping the active ingredient by the diluent, inwhich solid diluent is melted at a temperature below 80°-90°.

[0016] The method also allows the formulator to select a release rate ofthe active ingredient suitable for pest control and the characteristicsof the surrounding medium. For example, the release rate of the activeingredient through the capsule core can be adjusted by manipulating theamount or percentage of the diluent, distribution pattern of thediluent, method of entrapping the active ingredient in the diluent,physical properties of the diluent including its melting point, andtemperature of the surrounding medium. Furthermore, the release rate ofthe active ingredient through the shell can be adjusted by manipulatingthe composition and homogeneity of the capsule shell, thereby affectingthe size, length, density, tortuosity, distribution, and properties ofany pores in the shell and diffusivity of the active ingredient throughthe shell free of pores.

[0017] Ease of use or utility of the pest-control microcapsules preparedby any of the above methods can be improved by adding to the diluent awater-immiscible compound heavier than water and having at least oneester linkage in an amount effective to increase resulting density ofsaid microcapsules very close to 1.0. For example, the water-immisciblecompound can be added in an amount effective to make resultingmicrocapsules sink slowly in an aqueous solution or achieve naturalbuoyancy. Dense microcapsules prepared by these new methods will notfloat in an aqueous solution and will not form a creamed layer onstorage which has detrimental effects on ease of preparing the capsulesuspension for field applications.

[0018] The potency as well as the shelf life of the pest-controlmicrocapsules prepared by the above methods can also be improved byadding an antioxidation agent to the diluent and/or by adding a sunscreen such as carbon black or other UV absorbers.

[0019] As used herein, “core material”, of a microcapsule is thematerial in a microcapsule containing an active pest-control agent to becarried by the microcapsule and to provide effective pest control.

[0020] A “microcapsule shell” is, as used herein, the coating, membraneand/or wall that surrounds the volume material of the microcapsule inwhich the active ingredient is located. The microcapsule shell providesa physical barrier that separates the contents of the microcapsule fromthe exterior or surrounding medium in which microcapsules are immersedor placed.

[0021] A “pest-control agent” is any compound that is toxic to an insectat any stage of its development when ingested or brought into contactwith the target insects in some manner (e.g., pyrethroids), any agentthat disrupts mating of the target insects (pheromones), any agent thatalters the growth and development of insects at some stage of theirdevelopment (e.g., insect growth regulators), or any agent that acts asan attractant to a “trap” at which the insect is terminated in somemanner (e.g., by electric shock, drowning, or physical entrapment as ona sticky surface).

[0022] As used herein, a biopesticide is any active pest-control agentthat is nontoxic to mammalians. Examples of biopesticides include, butare not limited to, pheromones, pyrethroids, and insect growthregulators.

[0023] As used herein, “diluent” means a liquid or solid with a lowmelting point, for example, 80° C.-90° C., in which the activepest-control agent is soluble either at room temperature or below, atthe temperature at which microcapsule formation is carried out(typically at 40°-60° C.), or at the melting temperature of the diluent.Diluents may consist of a single chemical compound or may be a mixtureof several components where such diluents are natural products which intheir conventional form are composed of multiple components.

[0024] As used herein, toxicity generally pertains mainly to mammalians,therefore, plants and fruits treated by the nontoxic pest-controlmicrocapsules are edible.

[0025] Unless otherwise defined, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art related to this invention. Other methods and materialsin addition to those specifically described herein can be used in thepractice of the present invention. All publications, patentapplications, patents, and other references mentioned herein areincorporated by reference in their entirety. In case of conflict, thepresent specification, including definitions, will control. Thematerials, methods, and examples are illustrative only and not intendedto be limiting.

[0026] Other features and advantages of the invention will be apparentfrom the following detailed description, and from the claims.

[0027] The invention features a sustained-release, long-termpest-control microcapsule which is environmentally friendly andnon-toxic, and prolongs its potency by controlling the nature of thediluent in the capsule core in which the pest-control agent is dissolvedor dispersed.

[0028] In general, a microcapsule includes a capsule core and a capsuleshell, both of which can provide resistant paths to the mass transfer ofthe active pest-control agent contained in the capsule core. Thus, thepest-control microcapsule of the present invention is designed to reducethe rate of release of active ingredient distributed into thesurrounding medium, thereby reducing the cost of pest control as well asthe potential for environmental pollution by utilizing interactionsbetween the active ingredient and the diluent either in the solid orliquid state.

[0029] Diluents used in the microcapsule are selected from the class ofmaterials defined as lipids. Some may form liquid at room temperatureand below, while others form solids with low melting point, for example,lower than 80° C.-90° C. Most lipid diluents include one or more esterlinkages where one component of the ester linkage is a fatty acid whichis classified as either a short-, medium- or long-chained fatty acid.However, other components without any ester linkage, for example,cholesterol, can also be used as a lipid diluent.

[0030] Diluent lipids are often isolated from natural sources (e.g.,various plant and animal oils or waxes), are biodegradable, and arenon-toxic to all forms of life, thus, generally edible. Examples ofdiluent lipids include, but are not limited to, plant oils of commercesuch as corn oil, soybean oil, canola oil, peanut oil, olive oil, palmoil, coconut oil, cottonseed oil, and sunflower oil. Mixtures of theseoils as well as refined or purified oils obtained therefrom can also beused. Such oils refined for specific food or pharmaceutical applicationsmay be classified as oils rich in short-, medium- or long-chained fattyacids. Fats with low melting point produced by varying the degree ofhydrogenation of the aforementioned oils or isolated by selectivecrystallization from various plant oils can also be used. Oils derivedfrom an animal source such as butterfat oil, and low melting point fatsfrom animals such as butterfat and lard can be used as well, althoughsome animal oils may require additional stability control. Natural waxeslike bee wax (actually an insect wax produced by bees), carnauba wax (aplant wax), candellila wax (a plant wax), and paraffin wax can also beused. Mixture of these various oils, hydrogenated oils, and waxesderived from various plant or animal source can also be used. A purposeof mixing various oils and waxes is to alter the crystallizationtemperature of the waxes or hydrogenated oils, thereby altering thetemperature at which they soften.

[0031] Various aforementioned lipids are relatively pure compounds whichmay either be isolated from the above mentioned natural plant oil andwax sources or can be prepared by completely synthetic means. Examplesinclude triglycerides such as tristearin, tripalmitin, and trilaurin, aswell as triglycerides containing a mixture of one or more differentfatty acids. In addition, natural or formulated mixtures oftriglycerides, diglycerides, and monoglycerides with or without theadditional presence of various free fatty acids can also be used, forsuch mixtures in reality represent the actual composition of the variousplant lipids and animal oils aforementioned.

[0032] The formulator can customize the melting point of the diluent bymanipulating the size and chemical structure of the lipid. For example,the melting point of the lipid including oils, waxes, and fats can varyover a wide range of temperature by manipulating the number of esterlinkages as well as the number and characteristics of the short-,medium-, and long-chained fatty acids attached to those ester linkages.

[0033] The diluent is distributed in the core in such a manner that theactive pest-control agent is dispersed or dissolved in the diluent andmust diffuse through the resistant paths formed by the diluent to reachthe capsule shell through which it must subsequently diffuse in order tobe released from the capsules. The diluent may operate in several ways.One possible way is that the lipid and pest-control agent have a strongaffinity for each other (i.e., mutually miscible) and this affinityreduces the tendency for the pest-control agent to diffuse through theshell. In this case, the AI-lipid mixture may form a liquid at roomtemperature. Alternatively, the diluent may form a solid-like,matrix-like or mesh-like structure inside the core which effectivelyentraps the active ingredient inside such matrix and mesh, therebydelaying release thereof. Thus, a formulator can obtain desirablepermeability or release rate of the active ingredient by manipulatingseveral factors, such as the amount or percentage of the diluentcontained in the capsule core, distribution pattern of the diluent inthe core, method of entrapping the active ingredient in the diluent, andother chemical and/or physical properties of the diluent.

[0034] The sustained-release, pest-control microcapsule of the presentinvention may be made of biodegradable and nontoxic compounds. Thepest-control microcapsules can include in its core a bio-pesticide suchas pheromones, pyrethroids, and insect growth regulators as well as aninactive, biodegradable and nontoxic lipid diluent such as oils, waxes,and fats with ester linkages or cholesterol. However, conventional toxicpest-control agents can also be used along with the inactive,biodegradable, and nontoxic lipid diluent.

[0035] Examples of active, biodegradable, and nontoxic pest-controlagents include, but are not limited to, biopesticides such aspheromones, pyrethroids, insect growth regulators, and insectattractants or repellents. Conventional toxic pesticidal agents,however, can also be used in conjunction with the aforementionedinactive, bio-degradable, and non-toxic diluents.

[0036] The capsule shell separates the core volume material from thesurrounding medium, and provides the additional resistant paths, forexample, the shell pores and/or other paths, through which the activepest-control agent diffuses into the medium. Thus, permeability orrelease rate of the active ingredient can be manipulated by controllingat least one of the several factors such as the pore size, length,density, tortuosity, pattern of pore distribution in the shells, andother physical properties of the material constituting the shell.Details as to the formation of such capsule shells will be discussed ingreater detail below.

[0037] The microcapsules of the present invention may be formed by anyof the processes such as complex coacervation, solvent evaporation,interfacial polymerization (IFP), and in-situ polymerization. With IFP,multi-functional acid chloride and isocyanate are used as shell-formingagents. However, when the active pest-control agent contains afunctionality which may readily react with acid chloride or isocyanate,microcapsules can be formed by the processes such as complexcoacervation, in situ polymerization or solvent evaporation protocols.

[0038] Suitability of a given diluent/active pest-control agent forencapsulation can be defined by forming a series of mixtures of activepest-control agents with candidate diluents. When observed visually,they provide a means of assessing whether or not mixtures form ahomogeneous solution, and are mutually miscible or compatible. Forexample, following Examples 1 and 2 summarize some exemplaryobservations of compatibility of selected diluents and activepest-control agents.

EXAMPLE 1 Compatibility Test Results

[0039] MIXTURE COMPATIBILITY Beeswax (6 g) Formed a homogeneous solutionabove OFM* (6 ml) 60° C.; formed a mushy, soft solid when cooled to 22°C. Yellow Carnauba Formed a homogeneous solution above Wax (5 g) 70° C.;formed a very hard solid when OFM (5 ml) cooled to 22° C. HydrogenatedFormed a homogeneous solution above tallow (5 g) 40° C.; formed a softbut brittle solid OFM (5 ml) when cooled to 22° C. Candellila Formed ahomogeneous solution above Wax (5 g) 60° C.; formed a very hard solidwhen OFM (5 ml) cooled to 22° C. Paraffin Formed a homogeneous solutionabove Wax (5 g) 42° C.; formed a hard solid when cooled OFM (5 ml) to22° C. Dark chocolate Formed liquid at 22° C.; solidified at (5 g) 5° C.(i.e., in refrigerator) OFM (5 ml)

EXAMPLE 2 Compatibility Test Results Using Pheromone (CM)

[0040] MIXTURE COMPATIBILITY Beeswax (5 g) Homogeneous solution above55° C.; CM (5 ml) Solid at room temperature (22° C.) Yellow CarnaubaHomogeneous solution above 73° C.; Wax (5 g) Solid at 22° C. CM (5 ml)Hydrogenated Homogeneous solution above 41° C.; Tallow (5 g) Solid at22° C. CM (5 ml) Dark chocolate Liquid at 22° C. (5 g) Homogeneoussolution CM (5 ml) Candellila Homogeneous solution above 60° C.; Wax (5g) Solid at 22° C. CM (5 ml)

EXAMPLE 3 Evaluation Method Protocol

[0041] Miscibility of the active ingredient and diluents were furtherexamined by forming mixtures of various active ingredients (pheromones)with corn oil or triethylcitrate. The final composition of the mixtureproduced was 40 vol. % pheromones and 60 vol. % diluent (i.e., corn oilor triethyl citrate). The individual pheromones evaluated were: tomatopinworm, pink bollworm, leafroller, oriental fruitmoth, and coddlingmoth. All of these pheromones were completely miscible at roomtemperature in corn oil or triethylcitrate (40 vol. % pheromones/60 vol.% diluent). It was notable that coddling moth pheromones formed solid atroom temperature, but dissolved freely in both corn oil and triethylcitrate. In general, it was found that pheromones and pyrethroids weremutually miscible in the various diluents at a 40 vol. % activeingredient/60 vol. % diluent ratio.

EXAMPLE 4 Microencapsulation by Interfacial Polycondensation

[0042] Microcapsules were prepared using the core material which was amutually miscible mixture of the active ingredient and the diluent. Forexample, pink bollworm pheromone was dissolved in a purified lipid oil(Miglyol 812) such that the mixture contained 40 vol. % pink bollwormpheromone and 60 vol. % Miglyol 812. To this mixture (137 ml) was addeda multi-functional isocyanate (e.g., Mondur MRS) (27.4 ml). Theresulting mixture was emulsified in a aqueous medium that contained adispersing agent (e.g., partially hydrolyzed poly(vinyl alcohol—0.25 to5 wt. %). Once the desired oil phase droplet size was obtained, amulti-functional amine (e.g., ethylene diamine, diethylene triamine, ortriethylene tetramine) was added to the aqueous phase to therebyinitiate formation of a capsule shell. The reaction responsible forformation of a polyurea capsule shell was allowed to proceed for afinite time period (e.g., 1-8 hours) at an elevated reaction temperature(e.g., 40°-60° C.). The microcapsules produced in this manner, whenisolated and dried with a small amount of solid drying aid like fumedsilica (e.g., Cab-O-Sil M-5), formed free-flowing powder which producedno visible stain when stored for a prolonged period on paper, evidencingthat the microcapsules did not leach their nonvolatile diluent core at afinite rate. Furthermore, the microcapsule powder remained as free-flowpowder when stored for prolonged periods in closed storage containers,further evidencing that the microcapsule shell formed had superiorbarrier properties.

[0043] The above microencapsulation protocol had been successfullyrepeated with leafroller, oriental fruit moth, and tomato pinworm withpheromones as the active ingredient. The amount and composition of thecore material were held constant in these encapsulation runs as was theactual encapsulation protocol. The success of this series of experimentsdemonstrated the microcapsules with superior barrier properties.

[0044] All of the above-mentioned pheromones can be substituted in thesame encapsulation protocol where shell formation occurs by interfacialpolycondensation, because all of these agents are stable compounds freeof reactive functional groups that are chemically reactive withcompounds such as isocyanates and acid chlorides. Since these latterreactive compounds are dissolved in the core phase along with thepheromone selected to be encapsulated with the diluent, such reactivefunctionalities will likely react with any functional group located onthe active pest-control agent. Because the aforementioned pheromones donot have a reactive functional group, there will not be any suchreaction. However, with other active pest-control agents, chemicallyreactive functionalities are present that may inhibit the formation ofmicrocapsule shells by interfacial condensation. An alternateencapsulation protocol may be used, and/or the extent of reactionbetween reactive acid chloride or isocyanate functionalities withreactive functionalities located on the active ingredient may be reducedto essentially zero to prevent formation of new molecular species withundefined biological activity and toxicity. Accordingly, microcapsuleshells with such active ingredient may be formed by an encapsulationprotocol other than interfacial polycondensation, for example, complexcoacervation and in situ polymerization of urea and/or melamine withformaldehyde, as illustrated in the following example.

EXAMPLE 5 Microencapsulation of the Active ingredient with ReactiveFunctionality

[0045] Coddling moth pheromone contains a hydroxyl functionality that ispotentially reactive with acid chloride or isocyanate functionalities.In situ polymerization was used to produce the microcapsule shells. Nocompounds with a reactive group were introduced into the core materialin order to cause formation of the microcapsule shells. All reactivecompounds responsible for capsule shell formation were located in theaqueous medium in which the core material was suspended or dispersed.

[0046] Coddling moth pheromone (35 mg) was dissolved in 59 ml Miglyol812, the diluent. The mixture was emulsified in 100 ml of an aqueoussolution of ethylene-maleic acid copolymer solution in which 7 g of ureaand 0.4 g of ammonium chloride were dissolved. Once the desired size ofdesired oil phase droplets had been reached, formaldehyde was added(17.5 ml 37% solution), the system was heated to 40-60° C., and wasallowed to react for 2-6 hours. The capsule produced in this manner,when isolated and dried with a small amount of solid drying aid likefumed silica (e.g., Cab-O-Sil M-5), formed a free-flowing powder whichproduced no visible stain when stored for a prolonged period on paper,evidencing that the microcapsules did not leach their non-volatilediluent core at a finite rate. Furthermore, the microcapsule powderremained as free-flow powder when stored for prolonged periods in closedstorage containers, further evidencing that the microcapsule shellformed had superior barrier properties.

[0047] A pest-control microcapsule can be composed in such a way thatthe permeability or release rate of the active ingredient depends uponthe melting point of the diluent and the temperature of the surroundingmedium. Lipids such as oils, waxes, and fats with at least one esterlinkage or cholesterol are used as diluents and incorporated into thecapsule core through microencapsulation. In general, these lipids havemelting points of 80°-90° C. or lower, or may gradually melt over a widerange of temperature when the diluents consist of a mixture of variouslipids with different melting points. Thus, when the temperature of thesurrounding medium rises near or above the melting point of the lipid,i.e., usually during the season and/or the time of the day with highinsect activity or mating, the lipid diluent begins to soften or meltand the active ingredient previously entrapped by those lipid diluent isreleased and diffuses into the medium at a higher rate. However, whenthe temperature falls below the melting point of these lipids and enoughto suppress insect activities, the lipid diluent hardens or solidifies,and effectively sustains the release of the active ingredient byre-entrapping the active pest-control agent in the hardening orsolidifying lipid.

[0048] In addition, the lipid has a high boiling point, e.g., higherthan 200° C. at atmospheric pressure with the possibility ofaccompanying decomposition and, therefore, hardly evaporates.Accordingly, the potency of the pest-control microcapsule can beeffectively prolonged adaptive to the temperature of the surroundingmedium. Example 6 illustrates the field test results of long-termpotency of the microcapsules, which was also presented at the 73rdAnnual Western Orchard Pest & Disease Management Conference, ImperialHotel, Portland, Oreg., during Jan. 6-9, 1999. Relevant portions of theProceedings, entitled, “Behavior of Microencapsulated Coddling Moth andOriental Fruit Moth Pheromone Formulations In California Field Test,”are incorporated herein by reference.

EXAMPLE 6 Field Test Results of Pheromone Formulations

[0049] Field studies were carried out in California to evaluate thebehavior of two microencapsulated coddling moth (CM) and twomicroencapsulated oriental fruit moth (OFM) pheromone formulations. TheOFM formulations (Formulations A and B) were applied at 20 gms. activesper acre to 10 acre blocks of almonds in Kern County, Calif., with atractor drawn sprayer on Jul. 6, 1998. The CM formulations (FormulationsC and D) were applied at 20 gms. actives per acre by helicopter to 10acre blocks of Serr walnuts in Tulare County, Calif., on Jul. 24, 1998.Four lure baited winged sticky traps placed in each treated block werechecked periodically for moth capture. Control traps (four forOFM-treated blocks and two for CM-treated blocks) were placedapproximately one mile upwind from the treated blocks. Reported trapcounts are mean values recorded at the time periods specified.

[0050] Table 1 contains trap count data for OFM-treated almond blocks.For the first 51 days post-spray, both formulations reduced the trapcount to zero. At days 63 through 93 post-spray, trap counts in bothtreated blocks remained low. During the first 93 days post-spray, atotal of four moths were caught in traps in the block treated withFormulation A while three moths were captured in the block treated withFormulation B during the same period. The trap count increasedsignificantly at 98 days post-spray. Thus, a single application of thetwo OFM-loaded microcapsule formulations reduced moth capture in thetreated almond blocks to a very low level throughout this period. Thisis attributed to their ability to release OFM at a finite ratethroughout the test. TABLE 1 Mean number of oriental fruit mothscaptured at various times after application of microencapsulated OFMpheromone formulations as a spray on almond trees at a rate of 20 gm.actives/acre. Mean number of moths captured Days after spraying 7 18 2838 51 60 72 81 93 98 Microcapsule formulation A 0 0 0 0 0 0.25 0 0.75 06.5 Microcapsule formulation B 0 0 0 0 0 0 0.25 0.25 0.25 2.5 Control 104.8 10.8 9.0 26.3 18.0 12.3 38.8 16.8 10.8

[0051] Table 2 contains trap count data for CM-treated Serr walnutblocks. Formulation C reduced the coddling moth trap count to zero for18 days post-spray. The mean trap count increased to 1.25 moths at 32days post-spray, but this still represented a 93.9% reduction in trapcount relative to control. Formulation D gave zero trap count for 11days post-spray, but the trap count at days 18, 32 and 47 post-spray wasreduced by 95-97% relative to control. Both microencapsulated CMpheromone formulations at days 53 and 62 post-spray gave trap countssignificantly higher than control. The reduction in trap count caused bythe microencapsulated CM formulations is taken as evidence that thecapsules released CM pheromone at a finite rate throughout the test.TABLE 2 Mean number of coddling moths captured at various times afterapplication of microencapsulated CM pheromone formulations as a spray onSerr walnut trees at a rate of 20 gm. actives/acre. Mean number of mothscaptured Days after spraying 11 18 32 47 53 62 Microcapsule formulationC 0 0 1.25 3.0 9.0 24.0 Microcapsule formulation D 0 0.25 0.75 0.5 12.7527.25 Control 17.5 9.5 20.5 11.0 8.5 13.0

[0052] The data in Tables 1 and 2 indicate that the microcapsuleformulations evaluated caused a significant reduction in the number ofcoddling or oriental fruit moths captured in traps over a prolongedperiod.

[0053] The observations reported here might be unique to the conditionsthat existed in California during the test. No rain fell on any of thetest blocks throughout the test period. Furthermore, temperatures in theregion of the test blocks were high throughout much of the test period.Daily high temperatures were primarily 35-40° C. and daily lowtemperatures were primarily 17-22° C. until day 72 post-spray of the OFMtest and day 53 post-spray of the CM test. In spite of these elevatedtemperature conditions, the microencapsulated CM formulations remainedhighly effective in causing trap count reduction for periods of 32-47days. This was significant, because CM pheromone was susceptible todegradation. Scanning electron micrographs of leaf surfaces showed thatthe CM capsules were in various stages of deterioration at approximately42 days post-spray.

[0054] The results reported here provide encouragement thatmicroencapsulated pheromone formulations capable of multi-month fieldlife could be produced and microcapsules loaded with pheromonessusceptible to degradation could remain active in the field for amulti-week period.

[0055] The pest-control microcapsule of the present invention may have adensity comparable to that of water. Generally, lipid diluents arelighter than water arid, therefore, microcapsules containing sufficientamount of such lipids float in an aqueous solution on storage. Thecreamed layer formed by clogged microcapsules may adversely affect thepotency and performance characteristics of the microcapsules.Accordingly, a water-immiscible compound, having at least one esterlinkage and having a density greater than that of water, may be added tothe lipid diluent in an amount effective to make the microcapsules sinkslowly in an aqueous solution. Such water-immiscible compound can alsobe added in an amount effective to achieve natural buoyancy of themicrocapsule. Examples of such dense lipids include triethyl citrate,tributyl citrate, and triacetin.

[0056] The pest-control microcapsule may also include one or moreantioxidants in the diluent as well as one or more sunscreen agentswhich are known in the art to block the action of light in some manner,for example, carbon black or UV absorbers. Addition of antioxidants orsunscreens may enhance the oxidative stability of the diluent and,therefore, prolongs potency of the microcapsule as well. Examples ofsuch antioxidation agent include vitamin E oil and synthetic food-gradeantioxidants.

[0057] It is to be understood that while the invention has beendescribed in conjunction with the detailed description thereof, that theforegoing description is intended to illustrate and not limit the scopeof the invention, which is defined by the scope of the appended claims.Other aspects, advantages, and modifications are within the scope of thefollowing claims.

What is claimed is:
 1. Sustained-release microcapsule for long-term pestcontrol comprising: a capsule core comprising an active pest-controlingredient and a diluent; and a capsule shell physically separating saidcapsule core from surrounding medium thereof, said diluent configured toentrap said active ingredient therein and to provide resistance to masstransfer of said active ingredient therethrough, said capsule shellcomprising a plurality of shell pores and configured to provideadditional resistance to mass transfer of said active ingredienttherethrough, wherein said mass transfer resistance existing in at leastone of said capsule core and said capsule shell depends on thetemperature of the surrounding medium.
 2. Microcapsule according toclaim 1, wherein said diluent is configured to form a structurecomprising at least one of a solid-like mesh, a solid-like matrix, and aliquid, and to entrap said active ingredient therein.
 3. Microcapsuleaccording to claim 1, wherein said diluent is an inactive,biodegradable, and nontoxic compound.
 4. Microcapsule according to claim1, wherein said mass transfer resistance to said active ingredientthrough said capsule core depends on at least one of the factorscomprising amount of said diluent, percentage of said diluent,distribution pattern of said diluent, method of entrapping said activeingredient in said diluent, physical properties of said diluentcomprising melting point thereof, and temperature of the surroundingmedium.
 5. Microcapsule according to claim 1, wherein said mass transferresistance to said active ingredient through said capsule shell dependson at least one of the factors comprising pore size, pore length, poredensity, pore tortuosity, pattern of pore distribution, physicalproperties of said pore comprising melting point thereof, physicalproperties of said capsule shell comprising melting point thereof, andtemperature of the surrounding medium.
 6. Microcapsule according toclaim 1, wherein said active ingredient is a biopesticide comprising atleast one of pheromones, pyrethroids, insect growth regulators, insectattractants, and insect repellents.
 7. Microcapsule according to claim1, wherein said active ingredient is a toxic pest-control ingredient. 8.Microcapsule according to claim 6, wherein said diluent is inactive,biodegradable and non-toxic lipid comprising at least one of oils,waxes, and fats.
 9. Microcapsule according to claim 8, wherein saidlipid comprises at least one of ester linkage and cholesterol. 10.Microcapsule according to claim 9, wherein said ester linkage comprisesat least one of a short-, medium-, and long-chained fatty acid. 11.Microcapsule according to claim 8, wherein said lipid has a meltingpoint lower than 90° C.
 12. Microcapsule according to claim 11, whereinsaid lipid comprises at least two different compounds and melts over acertain range of temperature.
 13. Microcapsule according to claim 8,wherein said lipid has low vapor pressure and a boiling point higherthan 200° C.
 14. Microcapsule according to claim 8, wherein said lipiddissolves said active ingredient in liquid state thereof. 15.Microcapsule according to claim 8, wherein said lipid is obtained fromat least one of the sources comprising minerals, plants, animals, andchemical synthesis.
 16. Microcapsule according to claim 15, wherein saidlipid comprises at least one of mineral oil, plant oil, animal oil,animal fat, butterfat oil, butter fat, lard, natural wax, beeswax,insect wax, candellila wax, paraffin wax, hydrogenated plant oils, palmoil, and coconut oil.
 17. Microcapsule according to claim 15, whereinsaid lipid is treated by at least one of the processes comprisingfiltration, purification, distillation, hydrogenation, and selectivecrystallization.
 18. Microcapsule according to claim 15, wherein saidlipid comprises at least one of mono-glyceride, diglyceride, andtriglyceride, said triglyceride further comprising at least one oftristearin, tripalmitin, and trilaurin.
 19. Microcapsule according toclaim 18, wherein said glyceride lipid comprises at least one of ashort-, medium-, and long-chained fatty acid.
 20. Microcapsule accordingto claim 1, wherein said active ingredient is dissolved in said diluentin liquid phase at a temperature lower than 90° C. prior to forming saidmicrocapsules.
 21. Microcapsule according to claim 1, wherein saidmicrocapsules are formed by at least one of the processes comprisingsolvent evaporation, interfacial polymerization, in-situ polymerization,and complex coacervation.
 22. Microcapsule according to claim 21,wherein at least one of multi-functional acid chloride and isocyanate isdissolved in said active ingredient and said diluent, and forms saidcapsule shell by one of said processes.
 23. Microcapsule according toclaim 21, wherein said capsule shell is formed by condensation offormaldehyde with at least one of urea and melamine at a pH lower than7.0.
 24. Microcapsule according to claim 22, wherein said activeingredient comprises a functionality readily reacting with at least oneof said acid chloride and said isocyanate, and wherein said microcapsuleare formed by a process comprising at least one of complex coacervation,in situ polymerization, and solvent evaporation.
 25. Microcapsuleaccording to claim 1, further comprising an antioxidation agent capableof enhancing oxidative stability of said diluent.
 26. Microcapsuleaccording to claim 25, wherein said antioxidation agent comprises atleast one of vitamin E oil, and synthetic antioxidants.
 27. Microcapsuleaccording to claim 1, further comprising a sun screen agent capable ofenhancing light stability of said diluent.
 28. Microcapsule according toclaim 27, wherein said sunscreen agent is carbon black.
 29. Microcapsuleaccording to claim 8, wherein said diluent comprises a water-immiscibledense lipid having at least one ester linkage and having density greaterthan that of water, said compound configured to increase the density ofsaid microcapsules and to prevent said microcapsules from forming acreamed layer in solution thereof during storage.
 30. Microcapsuleaccording to claim 29, wherein said water-immiscible lipid is at leastone of triethyl citrate, tributyl citrate, and triacetin. 31.Microcapsule according to claim 29, wherein said water-immiscible lipidis added to said diluent in an amount effective to make saidmicrocapsule sink slowly in said aqueous solution.
 32. Microcapsuleaccording to claim 29, wherein said water-immiscible compound is addedto said diluent in an amount effective to achieve natural buoyancy ofsaid microcapsules.
 33. Sustained-release microcapsule for long-termpest control made by the process of: dissolving an active pest-controlingredient with an inactive, biodegradable, and non-toxic diluent toform a mixture; entrapping said active ingredient inside said diluent;microencapsulating said mixture in order to form a plurality ofmicrocapsules comprising capsule cores and capsule shells; providingresistant paths for mass transfer to said active ingredient to at leastone of said capsule core and said capsule shell, wherein said masstransfer resistance depends on the temperature of the surroundingmedium.
 34. A method of long-term pest control comprising the steps of:dissolving an active ingredient with an inactive, biodegradable, andnon-toxic diluent to form a mixture; entrapping said active ingredientby said diluent; microencapsulating said mixture in order to form aplurality of microcapsules comprising capsule cores and capsule shells;providing resistant paths for mass transfer of said active ingredient insaid capsule core and through said capsule shells; and sustaining therate of release of said ingredient through said capsule core and saidcapsule shell depending on the temperature of the surrounding medium.35. Pest-control method according to claim 34, wherein said dissolvingstep further comprising: melting said diluent at a temperature below 90°C.; dissolving said active ingredient; and providing said mixture ofsaid active ingredient and said diluent.
 36. Pest-control methodaccording to claim 34, wherein said microencapsulating step furthercomprising: manipulating at least one of amount of said diluent,percentage of said diluent, distribution pattern of said diluent, methodof entrapping said active ingredient by said diluent, physicalproperties of said diluent comprising melting point thereof, andtemperature of the surrounding medium; and varying said mass transferresistance to said active ingredient through said capsule core. 37.Pest-control method according to claim 34, wherein saidmicroencapsulating step further comprising: manipulating at least one ofpore size, pore length, pore density, pore tortuosity, pattern of poredistribution, physical properties of said pore comprising melting pointthereof, physical properties of said capsule shell comprising meltingpoint thereof, and temperature of the surrounding medium; and varyingsaid mass transfer resistance to said active ingredient through saidcapsule shell.
 38. Pest-control method according to claim 34, furthercomprising the steps of: adding a water-immiscible lipid to saiddiluent, said water-immiscible lipid heavier than water and having atleast one ester linkage in an amount effective to increase resultingdensity of said microcapsules very close to 1.0; forming saidmicrocapsule; and preventing said microcapsule from floating and forminga creamed layer on storage in an aqueous solution thereof. 39.Pest-control method according to claim 38, wherein the step of addingsaid lipid further comprising: adding said water-immiscible lipid tosaid diluent in an amount effective to make said microcapsule sinkslowly in said solution.
 40. Pest-control method according to claim 38,wherein the step of adding said lipid further comprising: adding saidwater-immiscible lipid to said diluent in an amount effective to makesaid microcapsule achieve natural buoyancy in said solution.
 41. Amethod of long-term pest control comprising the steps of: dissolving anactive ingredient with an inactive, biodegradable, and non-toxic diluentto form a mixture; microencapsulating said mixture in order to form aplurality of microcapsules including resistant paths for mass transferof said active ingredient; and sustaining the rate of release of saidingredient depending on the temperature of the surrounding medium.